If you wanted to buff ad assassins , you could have done it by buffing them..
Atleast that won't make non assassin champions abuse the lethality items such as
and
and even 
Atleast that won't make non assassin champions abuse the lethality items such as
and
and even 
garen needed the lethality buff tbh
This is riot games. AD assassins don't just receive straight buffs when they are struggling. It is either nerfs or they will buff the items so the adcs get a buff too. I know that sounds like hyperbole but im not kidding look at the changes to the ad assassins. They are mostly just nerfs with a buff so rarely seen it actually takes a while to find one and it is usually a small buff followed by a harsh nerf. In the entire history that ive played league i think the only time i saw zed get buffed was when he dropped to a 43% winrate and people were still saying he was broken and riot was destroying the game for buffing him...